Sliding doors and windows of the traditional or lift and slide type are well known, and basically comprise:                a fixed frame;        at least one mobile frame or sash which slides horizontally, opening and closing relative to the fixed frame;        at least one sliding unit or carriage associated with the bottom crosspiece of the sash and resting on a horizontal base track and designed to enable the sash to slide in both directions;        a control element located on the mobile frame and designed to actuate operating means which can be used to move closing means and to disengage the sash from the fixed frame so that it can be slid open, and, vice versa, when the upright of the sash is in contact with the upright of the fixed frame to stop the sash in a closed positioned;        the closing means therefore acting at least between the upright of the sash and the upright of the fixed frame (which, in the closed configuration are abutted against each other edge to edge).        
In the case of a lift and slide sliding door or window, the operating means allow disengagement of the closing means together with lifting of the sash relative to the carriage (so as to move weather strips located on the sash away from the track) and lowering of the sash at the sash closed position in order to return the weather strips to the position where they seal the door or window.
Current basic structures of a sliding sash for doors or windows combine a frame made of metal or synthetic material for perimetric closing of glazing with an inner insulating chamber.
The sash frame normally comprises four sectors (forming the two uprights and the two crosspieces) fixed together and on which the glazing is applied (having a flat perimetric profile).
The respective ends of the stretches of the frame are usually cut at 45° so that they can be joined (by special, known inner corner devices) to the corresponding end of the contiguous stretch.
Once this frame is complete, a set of machining operations is performed on it (cutting, slotting, boring, recessing, etc.) to create the housings or suitable passages for:                the control elements, that is to say, the handle,        closing means (catches or housings for them),        insertion of transmission means,        sliding carriages, and        stretches of operating rod for insertion in special channels.        
Therefore, a sash structured in this way may not just have a significant overall weight, but also an appearance that is not always acceptable due to the presence of the visible outer frame (depending on the rooms where it is installed) and high production costs, in particular due to the machining necessary for application of accessory elements which are essential for its movement and closing.